A protracted outbreak of Salmonella Hessarek infection associated with one brand of eggs­South Australia, March 2017 - July 2018

Salmonella Hessarek is an uncommon serotype in Australia. We report on the investigation of a protracted outbreak of 25 cases of S. Hessarek gastroenteritis in which cases were defined as any laboratory confirmed case of Salmonella Hessarek notified to the South Australian Communicable Disease Control Branch from 1st March 2017 to 3 July 2018. We conducted a descriptive case series investigation interviewing all cases and 17 (68%) reported consuming brand X free-range eggs. Four samples of one-dozen brand X eggs were cultured for the presence of Salmonella spp. One out of the four samples returned positive for S. Hessarek in the contents of the eggs; Salmonella was not present in any of the whole egg rinses of the four samples. The high proportion of cases reporting the consumption of brand X free-range eggs and the isolation of S. Hessarek from sampling four dozen brand X eggs is an unusually strong signal implicating brand X eggs as the source of this outbreak. From a public health perspective, it is important to understand the behaviour of S. Hessarek including its ability to be present in the content of eggs and further research is recommended. The findings in this investigation into a rare Salmonella serotype highlight the need for continuous monitoring of the epidemiology of Salmonella in Australia including the epidemiology of egg-associated Salmonella outbreaks of human disease.

Higher Storage Temperature Causes Greater Salmonella enterica Serovar Typhimurium Internal Penetration of Artificially Contaminated, Commercially Available, Washed Free Range Eggs.

Foodborne salmonellosis is a major public health concern, with contaminated eggs identified as a significant source of infection. In Australia, the most prevalent cause of salmonellosis from eggs is Salmonella enterica subsp. enterica serovar Typhimurium. This study explored the effect of temperature after 1, 7, 14, 21, and 28 days of storage on commercially available washed free range eggs, artificially contaminated with Salmonella Typhimurium on the external surface. At each time point, the external surface of the egg, the crushed eggshell, and the internal egg yolk and albumen were analyzed for Salmonella. After 28 days of storage, 25% of eggs stored at 4°C, 50% of eggs stored at 14°C, and 100% of eggs stored at 23 and 35°C were internally contaminated with Salmonella. After 1 day of storage, more than 50% of all eggs had Salmonella present in the crushed shell after the external surface had been disinfected with ethanol. This is the first study to demonstrate that refrigeration reduced the potential for Salmonella Typhimurium to penetrate the eggshell membrane and internally contaminate table eggs commercially available in Australia. It also suggests that the processes of cracking eggs may be a source of cross-contamination within the kitchen.